A190267 Numbers n such that d(n-1) = d(n+1) = 6, where d(k) is the number of divisors of k (A000005).

19, 51, 243, 244, 424, 476, 604, 638, 723, 846, 926, 1683, 1774, 2008, 2524, 2526, 2528, 3124, 3176, 3178, 4204, 4476, 4526, 4924, 5824, 6726, 6812, 6963, 7300, 7443, 7676, 8426, 8958, 8974, 9458, 9926, 10052, 10083, 10468, 11674, 11710, 12428, 12483, 12592

Offset

1,1

Links

Nathaniel Johnston, Table of n, a(n) for n = 1..2500

Maple

with(numtheory): A190267 := proc(n) option remember: local k: if(n=1)then return 19:else k:=procname(n-1)+1: do if(tau(k-1)=6 and tau(k+1)=6)then return k: fi: k:=k+1: od: fi: end: seq(A190267(n), n=1..44); # Nathaniel Johnston, May 06 2011

Mathematica

Mean/@SequencePosition[DivisorSigma[0, Range[15000]], {6, _, 6}] (* Harvey P. Dale, Jan 10 2025 *)

Crossrefs

Cf. A030515, A189974.

Sequence in context: A267572 A378179 A349554 * A373008 A066775 A118591

Adjacent sequences: A190264 A190265 A190266 * A190268 A190269 A190270

Keyword

nonn

Author

Juri-Stepan Gerasimov, May 06 2011

Status

approved